In signal transmitters, it is often desirable to up-convert broadband VHF signals (30-80 mHz to the EHF range (30-100 GHz) with medium to high power outputs. Similarly, in receivers it is desirable to similarly traverse the frequency range in the opposite direction.
A problem in accomplishing such conversions is that in the process of the frequency conversion, the heterodyned outputs exhibit sidebands which are so close to the baseband that they cannot be distinguished or filtered out. For instance, assuming it is desired to up-convert a 50 mHz signal to 30 GHz, a 29.95 GHz local oscillator is used with the result being the generation of not only the additive frequency (30 GHz) but also of the difference frequency (29.90 GHz). In addition, a number of lesser amplitude sidebands, each one 50 mHz less or more in frequency, are respectively generated. Filters are not available, at a reasonable cost, to select out the desired frequency products.
The prior art, as a result, has accomplished such frequency conversions by translating up an input frequency in a number of smaller steps so that the desired modulation products could be filtered at each step of up-conversion, the steps being repeated over and over again. Even in such systems, however, the multiple filterings tended to allow propagation of unwanted close-in sidebands. Thus, when the final up-converted signal was achieved, it included a number of unwanted spurious frequencies. If it was then desired to utilize that signal to synchronize an output oscillator, it was extremely difficult, if not impossible to assure that the output oscillator locked onto the desired frequency.
It is known that a free running Gunn or Impatt oscillator will lock onto any signal in the vicinity of its free running oscillation frequency. In fact, if the injected signal is sufficiently large, it can pull in the free running signal of the oscillator to achieve frequency lock, even if the injected signal is as much as 5% away, (depending upon the Q of the oscillator). If there are multiple frequency signals in the vicinity of the free running oscillator's frequency, the oscillator will lock onto the closest signal if all signals are of the same or similar levels or to the closest signal that has sufficient amplitude.
Accordingly, it is an object of this invention to provide a single stage, VHF to millimeter wave (and vice versa) frequency converter.
It is a further object of this invention to provide a single stage, broadband frequency converter wherein the output signal frequency is closely controlled.